Preliminary results of three-dimensional simulations of compressible Rayleigh-Taylor instability and turbulent mixing in an ideal gas using the piecewise-parabolic method (PPM) (with and without molecular dissipation terms) are presented. Simulations with spatial resolutions up to 512{sup 3} were performed. Two types of convergence studies are presented. Statistical analyses of the data are discussed, include: 1: spectra, and; 2) horizontally-averaged terms in the kinetic energy and onstrophy density evolution equations. The application of this statistical data to the development and testing of subgrid-scale models appropriate for compressible Rayleigh-Taylor instability-induced turbulent mixing is discussed.

Preliminary results of three-dimensional simulations of compressible Rayleigh-Taylor instabilities and turbulent mixing in an ideal gas using the piecewise-parabolic method (PPM) with and without molecular dissipation terms are presented. Simulations with spatial resolutions up to 512 were performed. Two types of convergence studies are presented. The first investigates the Reynolds numbers for which the simulations with molecular dissipation are converged with respect to spatial resolution, and the second investigates whether PPM simulations at different spatial resolutions reproduce fully-resolved PPM simulations with molecular dissipation. Finally, statistical analyses of the data are discussed, including spectra and horizontally-averaged terms in the kinetic energymore » and enstrophy density evolution equations. The application of this statistical data to the development and testing of subgrid-scale models appropriate for compressible Rayleigh-Taylor instability-induced turbulent mixing is discussed.« less

Inertial confinement fusion (ICF) implosions, whether real or ideal, are subject to a variety of hydrodynamic instabilities that amplify small departures from spherical symmetry. Asymmetric implosions departing from spherical symmetry can lead to the breakup of the imploding shell or the creation of hydrodynamic turbulence. In an effort to understand the evolution of the asymmetries, perturbation seeds with both velocity and surface displacements have been introduced at the boundary of two different density media to model analytical Rayleigh-Taylor instability growth. Growth of perturbed amplitudes has been studied in linear and late-time nonlinear regimes. Simulated linear growth rates and nonlinear bubblemore » velocities are in good agreement with theoretical values for Atwood numbers that are close to unity (relevant to ICF applications).« less

A spectral/compact finite-difference method with a third-order Adams-Bashforth-Moulton time-evolution scheme is used to perform a direct numerical simulation (DNS) of Rayleigh-Taylor flow. The initial conditions are modeled by parameterizing the multi-mode velocity and density perturbations measured just off of the splitter plate in water channel experiments. Parameters in the DNS are chosen to match the experiment as closely as possible. The early-time transition from a weakly-nonlinear to a strongly-nonlinear state, as well as the onset of turbulence, is examined by comparing the DNS and experimental results. The mixing layer width, molecular mixing parameter, vertical velocity variance, and density variance spectrummore » obtained from the DNS are shown to be in good agreement with the corresponding experimental values.« less